This site has a ton of information. The name doesn't do it justice in my opinion. It isn't the usual kind of site where the author tells you to disable tons of services and modify settings in the registry, etc.
On the site there is a free download called the Tweaking Companion [177 pages, PDF format].
It describes every aspect of Windows and PCs in detail using easy to understand language.
Discusses what the default settings are and why they are set that way
Indicates which settings you can change and what to expect [good or bad] if you modify them.
But for me the best part is the comprehensive information about WindowsXP
One of the many neat features in the guide is that there are many links you can follow for more information. For instance if you're in the drivers section there are links to places to find the latest drivers such as the vendor's site. There are also a lot of links to helpful software [usually free] for using with the guide or to enhance Windows or the PC.